1. Field of the Disclosure
The present invention relates to back light units, more particularly, to a light emitting diode (LED) back light unit having a light source module with a diffusing plate which has a light diffusing unit on a surface of the diffusing plate opposite to the light source.
2. Discussion of the Related Art
As the society is developing into an information oriented society, demand on display devices is being increased in a variety of forms. In response to the increase in demand, various flat display devices such as LCD (Liquid Crystal Display), PDP (Plasma Display Panel), ELD (Electro-Luminescent Display), VFD (Vacuum Fluorescent Display) are researched and developed, and some are already being utilized today.
The liquid crystal display device is a typical flat display device, which is mostly used as mobile image display devices and other devices such as notebook computer screens, TV sets, and computers monitors, owing to its advantages of good picture quality, light weight, thin profile, and low power consumption.
However, since the liquid crystal display device cannot emit light on its own, the liquid crystal display device requires an external light source to produce a high quality picture.
Therefore, in addition to a liquid crystal display panel, the liquid crystal display device is provided with a back light unit as a light source to provide uniform supply of high luminance light to the liquid crystal display panel to produce a high quality picture.
In general, as the light source of the back light unit, a cylindrical fluorescent lamp such as CCFL (Cold Cathode Fluorescent Lamp), HCFL (Hot Cathode Fluorescent Lamp) and EEFL (External Electrode Fluorescent Lamp); LED (Light Emitting Diode) devices; or EL (Electro Luminescence) devices are mostly used. Also, the back light units are divided into an edge-lighting type and a direct-lighting type back light units, according to arrangement of the light source.
Referring to FIG. 1, the edge-lighting type back light unit 10 is provided. A light plate 11 for scattering the light to make the light uniform is provided at one side of a fluorescent lamp 12, which is the light source of the back light unit. Also, a lamp housing 13 surrounds the fluorescent lamp 12.
The light from the fluorescent lamp 12 is reflected at the lamp housing 13 and is incident on the light plate 11.
Under the light plate 11, there is located a reflective member 14, and above the light plate 11, there are located various kinds of optical sheet unit 15 such as a diffuser sheet, a prism sheet, a protective sheet, and so on.
In the edge-lighting type back light unit, the light from the fluorescent lamp 12 is incident on the light plate 11, the light plate 11 scatters and converts the light incident thereon from a linear light into a uniform planar light, and the reflective member 14 under the light plate 11 reflects the light toward an upper side of the light plate 11.
The the various kinds of optical sheet unit 15 such as the diffuser sheet, the prism sheet and so on above the light plate 11 converges, and then diffuses the light again to improve the characteristics of the light such as a luminance and uniformity, and directs the light toward the liquid crystal display panel (not shown) on an upper side of the optical sheet unit 15, thereby functioning as the back light unit.
The edge-lighting type back light, unit which spreads the light from the fluorescent lamp at an edge of the liquid crystal display panel to an entire surface by using the light plate, has a low luminance and is difficult to apply to a large sized liquid crystal display device as compared to a direct-lighting type back light unit.
On the other hand, referring to FIG. 2, the direct-lighting type back light unit 20 is provided with the various kinds of optical sheet unit 25 stacked on a diffuser plate 21, which is added with a diffusing agent for diffusing light to make the light uniform. Fluorescent lamps 22 and a reflective member 24 is provided in a space under the diffusing plate 21, covered with a cover bottom 23 of the back light unit.
The direct-lighting type back light unit having the fluorescent lamps arranged on plane under the diffusing plate has a better light efficiency than the edge-lighting type back light unit since the light from the fluorescent lamps is directed toward the liquid crystal display panel directly, and can easily be applied to a large sized liquid crystal display device. However, it is liable to shapes of the fluorescent lamps being shown on the liquid crystal display panel.
In order to prevent the shapes of the lamps being shown on the liquid crystal display panel, securing and maintaining an adequate space between the fluorescent lamps and the diffusing plate and adding the diffusing agent to the diffusing plate for uniform distribution of the light is required. As a result, a total thickness of the back light unit becomes thicker, limiting fabrication of thinner liquid crystal display devices.
That is, the requirement for securing a predetermined space between the light source and the optical sheet unit for uniform light distribution limits fabrication of thinner liquid crystal display devices.